Coated aluminum product



Patented Jan. 25,1938

um'rsosrn'res PATE T OFFICE V 2,106,259

COATED imonuc'r Otto Stockmar, Hanover, Germany, asalgnor to Vcreinigte Lelchtmetallwerke G. m. b. 11-, Hanover-Linden, Germany, a corporation Germany No Drawing. Application July 24, .1936, Serial No. 92,369. In Germany July 25, 1935 Claims (on? 29-181) The present invention relates to coated aluml cially when the articles were annealed. The 'exnum products, and more particularly to coated perience oi the art with these alloy protective aluminum alloys with a corrosion resistant procoatings was practically the same as with pure tective layer having high tensile strength. aluminum. The reduction of corrosion resist- 5 It is well known in the art that theproblem ance of such magnesium-manganese alloys as 5 of utilizing aluminum in the structural field has with pure aluminum coatings was probably due been divided into two parts. One problem conto the diflusion of copper from the baseelement cerned the production of aluminum alloys of high into the protective coating. This diilusion betensile strength and the other concerned incame particularly noticeable when annealing such creasing the corrosion resistance of aluminum composite articles-because in annealing aluminum 10 products. The p'roblem oi increasing the tensile alloys containing copper and magnesium, tem' strength of aluminum products-was met by the j peratures above 400 C. were required and at introduction of various alloys, such as the durthese temperatures there was some softening of aluminums. However, such\ alloys have unthe alloys. In as much as the protective coatfortunatelybeen subject to more corrosion than ing had to be as thin as possible in order to rer pure. aluminum. It seemed that as the tensile duce the loss of tensile strength, there was the strength increased the resistance to corrosion dedanger that copper might diffuse to the very creased. It was then suggested that aluminum surface'of the protective coating when the analloys having high tensile strength but ,a low healing operation was prolonged with the conresistance to corrosion should be clad with. an sequent loss of corrosion'resistance which the aluminum coating of high corrosion resistance. virgin coatingpossessed. Forthe purpose of re- This practice resulted in a sacrifice in tensile ducing or preventing the diffusion, and of main-' strength. It has been known that such a protaining the resistance to corrosion, it was sugtective coating has been-comparatively thin, but gested to interpose another layer between the base i 5 in the aircraft art even such a thin coating has element and the protec iv n T constituted an important part of the cross-seccreased the cost: of manufacture considerably. tion of the article, especially when the diflerence To es ape this difliclllty. attempts were made to g -in tensile strength'oi the base element and the use aluminum alloys containing 1 -to 4% mancoatinglis considerable. For example, a coating ganese, 0.5 to 6% magnesium, and up to 1% having a thickness of 5% of the cross-section of antimony. These protective coatings had the 30 the base element, the coating represented 10% shortcoming that copper had to be absent for of the total cross-section of the article. When wholly sati f y results: The xpl n on ol" pure aluminum was used as the coating, the loss this improvement was the subject-oi discussion in tensile strength can be appreciated by comand was thought to be the r s lt f he presence paring the tensile strength (10 kgms. per square of magnesium in the aluminum in solid solumillimeter) of pure aluminum with the tensile tion. However, no oneventured to suggest that strength kgms'. per square millimeter) of the use of high magnesium content alloys or the duraluminunn This loss in tensile strength has in eas of t magnesium-content. a been known to constitute an important factorin would result in almostcomplete elimination of 0 the construction of aircraft. The realization of diffusion of copper into the protective layer while the importance of suchaloss led to the proposal to at the same time retaining an equal measure of 9 use alloys such as those which contain about co osio re ta ce and tens e s rength. The 1% magnesium and about 1% manganese having expert authorities in this field rejected the suga tensile strength of about 20 to about 22 kgms. gestlon that alloys containing more magnesium 45 per square millimeter and possessing resistance would be more resistant to diifusion and thus toto corrosion as a protective coating. However, it lowering of the corrosion resistance as unlikely.

was recognized very quickly that such alloys had As a matter of fact, one expert authority known little chance of greater success since the resistthroughout the world for his researches in the ance of the protective coating to corrosion was refield oialumlnum alloys, stated that he had little duced after application to the base element,especonfidence in the so-called "high magnesium 50 particularly because of manufacturing difilculties. There seemed to be no reason to expect that increasing 'the magnesium content above 6%v would make any marked improvement inthe qualities of the alloy. The use of magnesiumaluminum alloys of the magnalium type as protective coatings for copper-aluminum alloys of the duraluminum type presented many manufacturing difliculties) Among them perhaps the most serious was the lowering of the resistance to corrosion of the protective coating on annealing and thereduction of the tensile strength of the coated article compared with the uncoated base element. Although many proposals have been made, none, as far as I am aware, has been wholly successful and satisfactory when carried into industrial practice for the production of commercial products. 20

I have discovered that a coated aluminum article may be produced the tensile strength of which is substantially as great as that of the base element and the corrosion resistance of the coating' is not substantially reduced even after annealing.

It is an object of the present invention to provide an article of manufacture with a protective coating for an aluminum alloy with a high resistance'to corrosion.

It is another object of the present invention to provide an article of manufacture with a protective coating for an aluminum alloy substantially insensitive to the diii'usion of copper.

It is a further object of the present invention to provide an article of manufacture with a protective coating of an aluminum alloy having a high tensile strength.

Other objects and advantages of the invention gill become apparent from the following descrip- Broadly stated, it has been discovered that the loss of resistance to corrosion of aluminum and aluminum alloy coatings on copper-bearing aluminum articles may be substantially. eliminated.

As a result of extended research and prolonged experimental investigation concerning the eiIect of increasing the magnesium content of aluminum alloys, an article constituted of a copperbearing aluminum alloy coated with an aluminum alloy of high corrosion resistance in which the corrosion resistance of the coating is not substantially reduced when in contact with the base element was found. Contrary to the beliefs of the art and the expectations and predictions of expert authorities, it has beendiscovered that a high magnesium alloy or a magnesium content above 6% does substantially-eliminate the reduction of corrosion resistance of aluminum alloy" coatings by practically: prohibiting the diffusion of copper from the base element into the protective coating. Thus, it is possible with the use of the presentinvention to produce a coated duraluminum article, for example, in which the magnesium aluminum alloy coating has substantially the same corrosion resistance as such a magnesium aluminum alloy has when not in contact with a. copper-bearing aluminum alloy. This discovery has the additional benefit of increasing the ease with which alloys of the duralumin Those skilled in the art willappreciate that this A is an important factor, particularly in the problem of aircraft design. The advantage is readily aluminum alloys containing up to 6% magnesium seen by comparing the tensile strength of duralumin with that of the various coatings In addition to a high tensile strength, aluminum alloys of the type containing more than 6% of magnesium have a Brinell hardness in excess of prior aluminum coatings.

The present invention contemplates coating aluminum alloy articles of high tensilestrength and comparatively low resistance to corrosion with aluminum alloys containing from about 6.5% to about 12% or 13% magnesium. Such coatings may be applied by any of the well-known methods, such as welding, rolling, etc. as those skilled in the-art know. In some instances, a binder of pure aluminum may be used, in welding such coated articles.

For the purpose of giving those skilled in the art a better understanding of the invention, the fol-- lowing illustrative examples will now be given.

A rolled plate, about '70 mm. thick, of an aluminum alloy containing 4% of copper, 0,6% of manganese, 0.5% of magnesium and the usual impurity content of silicon and iron is carefully cleaned by milling and brushing. Thereupon this plate is enveloped on all sides with a clean brushed sheet, about 5 mm. thick,-of a magnesium-aluminum .alloy, containing about 7% of magnesium and as free as possible from the usual impurities,

temperature of about 350 to 500. When the and'the whole is next heated in a furnace at a plate has been uniformly heated throughout and ..all parts thereof have reached this temperature,

about 0,5 mm. Only then is the sheet of mag nesium-aluminum alloy fitted around the plate, the whole being now brought to welding temperature and hot-rolled.

1 In addition to the alloys hereinbefore specified, such as contain about 3.5 to 4.5% Cu, 1.3% Mn,

1.1 to 1.3% Mg. and 0.4 to 0.8% $1 are suitable for the core alloy. Alloys containing only 4% of copper, 2% of magnesium and 2% of nickel,

i. e. the so-calied Y-alloys. may also be used as core material in view of their excellent strength properties.

Alloys high in magnesium are particularly suitable for'the covering metal. Apart from the alloys hereinbefore mentioned, there are those containing 7% and also those containing 8 or 9% of magnesium. Such alloys may also contain some manganese, say 0,8%.

After the plates have been rolled in usual manner the edges are trimmed ofl', whereupon the sheets of clad metal are ready for use.

The procedure is the same in the production of pressed sections. For this purpose the core and covering material, are placed inthe press one so i upon the other-and side by side in the usual 9,100,950 manner well known in the art, and then pressed all together.

Although the present invention has been described in connection with a preferred embodiment, it is to be understood that variations and modifications may be resorted to as those skilled in the art will readily understand. Such varia-' tions and modifications are considered to be with-.

in the purview and scope of the appended claims.

I claim:

1. As a new article of manufacture having high tensile strength and high corrosion resistance. a composite aluminum article comprising a base element of aluminum alloy containing copper and a welded coating of a magnesium-aluminum alloy substantially devoid oi zinc and containing more than about 6% to about 13% of magnesium s aid composite article having substantially the same tensile strength per unit of cross section as the uncoated base element.

2. As a new article of manufacture having high tensile strength and high corrosion resist-- ance, a composite article a of aluminum alloys comprising a base element of aluminum alloy containing copper having high tensile strength and low corrosion resistance and a coating of a magnesium-aluminum alloy substantially devoid of zinc and containing about 7% of magnesium,

said base and'said coating being joined by wclding said base, coating and an interposed sheet oioriginally pure aluminum having a thickness of about 1% of the thickness oi said base, and forming a composite article, said composite article having a tensile strength per unit of cross section substantially the same'a's' the uncoated base element.

3. As a new article of manufacture having high tensile strength and high corrosion resistance.

a composite article of aluminum-bearing material comprising a base element of aluminum alloy containing copper and an aluminum alloy substantially devoid of zinc and containing more than about 6% to about 12% of magnesium, said base element and said coating'being mutuallybonded by welding to a thin intermediate layer'oi originally pure aluminum.

4. As a new article of manufacture having high tensile strength and high corrosion resistance, a composite article comprising a base element oi aluminum alloy containing copper having high tensile strength and low corrosion resistance and a welded coating of an aluminum alloy substantially devoid of zinc and containing more than about 6% to about 12% magnesium.

5. As a new article of manufacture having high tensile strength and high corrosion resistance,

a composite article comprising a baseelement of aluminum containing copper. having high .ten-

sile strength and low corrosion resistance, a

coating of aluminum materiaisubstantialiy devoid oi zinc and containing more than about 6% to about 12% magnesium and an intermediate layer of originally pure aluminum, said base element and said coating being bonded by welding to said intermediate layer, said intermediate layer having a zone oidiflused copper from said base element anda zone of diffused magnesium from said coating inhibiting further diffusion of copper. 1 v

OTIO STOCKMAR. 

